Vaccines and/or bacterins (formalin inactivated whole cell suspensions) are widely used to prevent diseases in humans and other animals. They usually consist of the organism and/or its metabolites responsible for a particular disease problem. The organisms may be in either their natural form, dead whole cells or live or attenuated or in non-native forms comprised of structural subunits of the pathogen or crucial metabolites. Almost all gram negative bacteria have a heat stable cell wall structural component referred to as lipopolysaccharide (LPS), that may function as a protective antigen. That an immune response directed against these structural components is sufficient to protect the animal against subsequent challenge by the pathogen. As with other animals, fish reared for food also suffer from systemic diseases that require prevention and/or treatment.
These diseases are due to variety of pathogens, including viruses, bacteria, fungi, protozoans and metazoans. The types of diseases depend upon geography (where the fish are being reared), genetics (the species and genetic makeup), the environment (i.e., fresh versus brackish versus salt water) and the management/husbandry philosophies of those individuals rearing the fish. Disease prevention is always preferable to reactive disease treatment. Many of the primary bacterial pathogens that affect fish can readily be prevented by immunization.
Fish vaccines generally consist of formalin inactivated suspensions of whole cells. These preparations are diluted and administered to fish by injection or immersion. Alternative methods include bathing the fish in highly dilute suspensions or spraying fish directly with the diluted preparation, which is then absorbed through the gill membranes.
Virtually all commercially available fish vaccines are in liquid form and are prepared by either continuous culture or batch fermentation and are subsequently inactivated with formaldehyde. They are whole cell-based products that depend on a stable cell wall component (LPS) for their protective properties. Due to their liquid nature, these products have strict refrigeration requirements. Accordingly, a relatively short shelf-life can be expected and the products may become contaminated with extraneous organisms or even occasionally with living organisms contained in the vaccine, particularly if the container of the liquid product is opened and resealed improperly. The liquid products are also bulky and inconvenient to transport in large quantities. Furthermore, the use of liquid based bacterins in oral vaccine preparations may be hampered by rancidity problems, standardization of antigen levels and stability problems.
Exemplary of the currently available methods for the preparation of vaccines are the following:
U.S. Pat. No. 3,862,313 to Fryer et al. describes a wet whole cell vaccine of Vibrio anguillarum which may be administered orally or by injection. The actual preparation of the vaccine comprises growing the bacterial cells in a suitable medium, killing the cells by formaldehyde addition, harvesting the cells by centrifugation and finally freezing the resultant wet cells. For use, the frozen vaccine is thawed into a paste.
U.S. Pat. No. 3,755,557 to Jacobs teaches the use of lecithin as a stabilizer to disperse dry antigens in a liquid propellant for spray vaccines. The antigens must be worked up into the vaccine in a dry condition. The techniques of freeze-drying and vacuum drying are described.
U.S. Pat. No. 3,608,066 to Illartein describes a pharmaceutical preparation of finely ground, killed, lyophilized microorganisims and a suitable carrier. It is designed to be used in the upper and lower respiratory tracts. The preparation of the antigenic component includes heat killing and centrifuging the chosen bacteria, lysing the cells and then lyophilizing the resultant suspension by conventional means. The powdered antigen is then prepared into an aerosol formulation with a lubricant and a propellant.
U.S. Pat. No. 4,287,179 to Amend provides a liquid vaccine in which whole fish are immersed which comprises killed Yersinia ruckeri.
It is an object of the present invention to obviate or mitigate the above disadvantages.